In the interconnection of an electronic private automatic telephone exchange to a central office it is necessary to detect loop, ringing and tip lead ground currents. Conventionally these functions are accomplished by providing a separate detector for each of the above functions.
It is also known to utilize detector circuits which are connected to the ground and/or power supply of the automatic exchange. Such connections may result in limitations to the following parameters: Noise Immunity, Longitudinal Balance, AC Induction, Lightning protection, leakage current and hazardous voltages. Known circuitry does not enable interconnection to central offices having grounded ringers.